Pasture-raised animals eat a natural diet of grass (or bugs/worms for chickens) and graze on outside pastures.
Meat that is 100% grass-fed is higher in omega-3, vitamin A, vitamin E, and antioxidants like glutathione (8). Pasture-raised animals are more ethically raised because this form of agriculture is closer to their natural way of life. Buying grass-fed meat from local farmers is another way to ensure you are supporting ethical agriculture (as well as local, small farms).
Supplementing with grass-fed protein sources is an excellent way to get amino acids, iron, vitamin B12, zinc, and more!